The antiproteolytic activities of the blood plasma (BP) and cervical mucus (CM) determined as trypsin inhibiting activities (TIA) where trypsin served as a model serine protease, were variable after superovulatory stimulations of ewes and after their gamma irradiation (2.45 Gy). TIA's were determined from the reduction in the bovine trypsin hydrolysis of the low-molecular chromogenic substrate N-alpha-tosyl-L-arginyl-p-nitro anilide (TAPA) (Bartík et al., 1974). The inhibition was expressed in per cent when delta A405 = 1.0 for 10-minute incubation at 25 degrees C, pH = 8.05, 0.2 mol/l tris-HCl buffer, was taken as 100%. Student's t-test was used for the statistical evaluation. A hundred ewes of the Merino breed were applied Agelin vaginal tampons (20 mg chlor-superlutin per head) on day 1 for 10 days in the anoestric period (May). A part of these ewes were subjected to whole-body gamma irradiation on days 6 to 11. When the irradiation was completed and the tampons were taken out, the ewes (three to four years old lambing ewes, yearling ewes) were stimulated to superovulations by an administration of 1500 IU serum gonadotropin (SG) or 450 IU follicle stimulating hormone (FSH). These parameters were followed in the subsequent 5-6 days: BP TIA (Figs. 1 and 4), fraction of low-molecular BP (n) TIA (Figs. 2 and 5), CM TIA (Figs. 3 and 6). Fig. 7 shows the average values of the results. The lambing ewes and yearling ewes had various responses to irradiation and superovulatory stimulation. Gamma irradiation eliminated the increase in BP TIA (P < 0.001) in the ewes after stimulations (Fig. 1a, b). The yearling ewes showed nonsignificant changes (ns) as their responses to SG stimulations and gamma irradiation, but the responses on the particular days of the trial were different (Fig. 1c, d--FSH stimulation). Similar changes were observed in the BP nTIA fraction. The changes in the average values of CM TIA were nonsignificant in the lambing ewes, the gamma irradiation reduced CM TIA only after FSH stimulation (P < 0.002). The amount of cervical mucus decreased after stimulations and irradiation, the thickness of ovarian epithelium and muscles was reduced in the particular parts, differently in lambing ewes and in yearling ewes.(ABSTRACT TRUNCATED AT 400 WORDS)